Herbicidal method utilizing phenyl 2, 3, 6-trichlorophenylacetate



United States Patent 3,318,682 HERBICIDAL METHOD UTILIZING PHENYL 2,3,6- TRICHLOROPHENYLACETATE Jack S. Newcomer, Wilson, Edward D. Weil, Lewiston, and Edwin Dorfman, Grand Island, N.Y.. assignors t0 Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed May 20, 1965, Ser. No. 457,524 3 Claims. (Cl. 71--2.6)

This application is a continuation-in-part of Ser. No. 101,061, filed Apr. 6, 1961, now United States Patent 3,215,729, which is a continuation-in-part of Ser. No. 730,051, filed in the United States Patent Office, Apr. 22, 1958, now abandoned.

This invention relates to the use of herbicidal compositions of matter derived from 2,3,G-trichlorophenylacetic acid and to a process for preparing them. More specifically, it is of a herbicidal method utilizing the aromatic esters of 2,3,6-trichlorophenylacetic acid, which have superior characteristics as herbicides and soil sterilants, as compared to the 2,3,6-trichlorophenylacetic acid and ts esters of the aliphatic monohydric alcohols.

In accordance with this invention, there is provided a method for controlling the growth of plants which comprises applying to the locus to be treated a herbicidal amount of at least one aromatic ester of the formula:

CHzCOOR wherein R is an organic aromatic radical generally containing from 6 to 18 carbon atoms and preferably from 6 to 15 carbon atoms. The preferred aromatic radicals are selected from the group consisting of phenyl substituted phenyl, naphthyl and substituted naphthyl, wherein the substituted groups of the substituted phenyl and naphthyl radicals may vary from 1 to 5. The most preferred radical is phenyl. The substituent groups are preferably selected from the group consisting of halogen, especially bromine and chlorine, hydroxy, carboxy, nitro, amino, and alkyl containing 1 to 8 carbon atoms.

Among the many compounds intended to be within the purview of this invention are:

phenyl 2,3,6-trichlorophenylacetate,

cresyl 2,3,6-trichlorophenylacetate, pentachlorophenyl 2,3,6-trichlorophenylacetate, p-chlorophenyl 2,3,6-trichlorophenylacetate, o-chlorophenyl 2,3,6-trichlorophenylacetate, 2,4-dichlorophenyl 2,3,6-trichl0rophenylacetate, 2,4,5 -trichlorophenyl 2,3,6-trichlorophenylacetate, 2,4,6-trichlorophenyl 2,3,6-trichlorophenylacetate, o-hydroxyphenyl 2,3.o-trichlorophenylacetate, ,B-naphthyl 2,3,6-trichlorophenylacetate, ot-naphthyl 2,3,6-trichlorophenylacetate, p-tert-butylphenyl 2,3,6-trichlorophenylacetate, o-carboxyphenyl 2,3,6-trichlorophenylacetate, o-octylphenyl 2,3,6-trichlorophenylacetate, p-octylphenyl 2,3,6-trichlorophenylacetate, and resorcinol bis (2,3,G-trichlorophenylacetate).

The high cost of labor and farm machinery have made the hand or machine suppression or eradication of weeds economically unfeasible. For this reason, there has become an increasing tendency on the part of growers to rely more and more on chemical control of weeds through the use of herbicides. Since herbicides structurally comprise many diverse classes of substances, it is not suprising that different crops differ markedly in their sensitivity or resistance to the vast number of herbicides now in commercial use. Thus, while a high degree of phytotoxicity 3,318,682 Patented May 9, 1967 against a broad spectrum of Weeds, selectivity and ease of formulation are still the sine qua non of a herbicide, the volatility and persistance of a herbicide play an important part in its commercial acceptance. High volatility,particularly, is a serious drawback to the use of herbicides in areas where there are herbicide-sensitive crops planted close to an area in which herbicide use is desired. For example, 2,4-dichlorophenyoxyacetic acid (2,4-D), and its esters, are especially phytotoxic toward certain broadleaf crops, such as cotton, soybean, tobacco and tomatoes. Unfortunately, 2,4-D and especially its esters also have a relatively high volatility, thus through natural vaporization considerable quantities of this herbicide are carried for rather long dstances from the place of application. Thus, in many instances, susceptible crops have been damaged through the vaporized herbicide causing heavy financial loss to the crop and grower. For this reason, in many areas of the country the use of 2,4-D and especially its ester, is restricted or prohibited. This is especially true in areas where cotton, tomatoes, tobacco and truck crops are important. Unlike 2,4-D, the volatility problem of 2,3,6-trichlorophenylacetic acid cannot be corrected by making the less volatile .aliphatic monohydric esters. The reason for this is that while the volatiltiy of the simple aliphatic esters is reduced as the chain length increases, there is a corresponding large re duction of herbicidal activity making the esters of higher aliphatic monohydric alcohols of little commercial value. Unexpectedly, it has been found that the compositions of this invention not only have low volatility, but retain their high degree of herbicidal activity, thus enabling these novel herbicides to be used where 2,4-D, 2,3,6-trichlorophenylacetic acid and the aliphatic monohydric alcohol esters of 2,3,6-trichlorophenylacetic .acid would be precluded.

Perhaps even more unexpected than the discovered superiority of the phenyl esters over the 2,3,6-trichloro phenylacetic acid and its aliphatic esters, is the finding that of the entire class of phenyl, substituted phenyl, naphthyl and polysubstituted phenyl esters of 2,3,6-trichlorophenylacetic acid encompassed by this invention, the simple unsubstituted phenyl ester of 2,3,6-trichlorophenylacetic acid is superior to the substituted phenyls. This superiority of the unsubstituted phenyl ester is particularly surprising in view of the well known observation that substitution in the aromatic ring of phenyl and benzoic acids increases herbicidal activity, partcularly halogen substitution. No explanation of this anomaly is offered.

It is further surprising that the phenyl ester may be made in good yield by direct esterification of the acid by phenol. It is well known that the esterification of carboxylic acids by phenols is generally unsuccessful and that the more expensive route via the carboxylic acid chloride or an hydride must usually be resorted to in order to prepare phenyl esters.

While low volatility is an important attribute of the compositions of this invention, an equally important advantage of these herbiicdal compositions is that their phytotoxicity toward many weeds persists for long periods of time after their application to the soil. As in the case of low volatility, the reason for this long term persistence in the soil is not obvious or well understood. For this reason, no theory of operation or mechanism is advanced, but it is a major factor in the value of these compositions as soil sterilants, in volume crops such as sugar cane where frequent hand or grabbing mechanical cultivating is economically prohibitive. In addition, these compositions, because of the low cost and high phytotoxicity toward a variety of weeds and grasses are especially useful as soil sterilants on low grade land such as public and private thoroughfares, road shoulders, railroad beds,.rights of way, and drainage and irrigation ditches. The compositions are especially phytotoxic toward weeds and grasses including among others, quackgrass, wild bluegrass, Iohnsongrass, wild carrot, ragweed, chicory, Canadian thistle, plantains, oxalis, daisy, yarrow, foxtail, field bindweed, hedge bindweed, milkweed, mustard and dock. An ancillary effect of the low volatility and long lasting phytotoxicity of the inventive compositions is that they are especially advantageous in areas of high rainfall or in drainage and irrigation ditches where conventional herbicides, such as the free 2,3,6-trichlorophenylacetic acid are leached out or lose their effectiveness. Thus, in crops such as pineapple, sugar cane, and the like, the herbicide need only be applied once during the growing season to effect full control of the weed population.

The compounds of this invention may be utilized as either the highly purified product or as the technical crude as well as states of purity intermediate to these purity extremes. They may be applied by themselves or diluted with liquid or solid carriers or diluents. Other herbicides, fungicides, insecticides or soil sterilants may be used as the diluents. For example, the compositions may be combined with other herbicides such as the 2,4-dinitro-6-alkyl phenols, pentachlorophenol, ammate, the phenylureas, N-m-trifluoromethylphenyl N'-N' dimethylurea, N- chlorophenoxyphenyl-N-N-dimethylurea or diurea, the triazines such as 2,4-dialkylamino6-chloro-sym-triazine, 2,4-dialkylamino 6 methoxy-sym-triazine, 2,4-dialkylamino-6-methylthio-sym-triazines, the chlorophenoxy aliphatic acids, the trichloroacetates, the chlorates, borates, dichloropropionates, S-alkyl-N, N-dialkylthiocarbamates, u-chloro-N-substituted acetamides, oc-ChlOIN,N-diS11bSlituted acetamides, such as a-chloro-N,N-dialkyl acetamide, the chlorobenzoic acids such as trichloroand polychlorobenzoic acids, trichloroaminopicolinic acid, aminotriazole, diphenylacetamides, dichlorobenzonitriles, herbicidal uracils, 3-amino-2,5-dichlorobenzoic acid and the like. Optionally, the compositions may be combined with fungicides such as sulfur, capstan or the metal dimethylthiocarbamates. Typical compatible insecticides are malathion, chlordane, DDT, benzene hexachloride and the like. Soil sterilants, such as the alkali and alkaline earth metal chlorates and borates, the above-mentioned triazines and ureas, appear to have an enhanced effect, greater than additive, by combination with inventive compositions.

The compositions of this invention readily lend themselves to formulation ranging from the simple to most complex. They maybe mixed with the conventional pest control and herbicide adjuvants, modifiers, diluents or conditioning agents so that they may be formulated as solutions, emulsions, dispersions, wettable powders or dusts. The diluents may be solids of varying particle size, such as sawdust, clay, earth, mica, cereal flours, starches, diatomaceous earth and the like. Typical liquid carriers among others are water, petroleum fractions, liquid aliphatic or aromatic alcohols; esters, glycols and ketones. The liquid formulations whether solutions or dispersions, emulsions or wettable powder dispersions, may contain as a conditioning agent one or more surface active agents in amounts sufficient to impart the desired characteristics to the formulation. By the term surface active agent are included wetting agents, dispersing agents, emulsifying agents and the like. A list of such agents may be found in Detergents and Emulsifiers, published by John W. McCutcheon, Inc., Morristown, N.J., 1962.

There is considerable latitude and variation possible as to the mode and time of application of the inventive herbicidal compositions. For example, the compositions may be hand or machine broadcast, or disced or plowed into the soil or applied as a foliar spray or as a spray on the soil. The preferred procedure is to broadcast or spray the compositions on the soil prior to weed emergence. There is no special or critical time of application, this being largely determined by the convenience and preference of the user, except in the case of use in sugar cane where the preferred timing is at planting, at spring cultivation or at layby.

Similarly, the rate of application of the herbicidal composition is varied from one-half to one hundred pounds per acre, usually within the range of one to fifty pounds per acre, dependent upon several factors such as soil structure, climatic conditions, the stage of growth of the weed and crop, the type of weed or crop as well whether sterilization or mere eradication of the weeds is sought. The preferred application rate, depending upon so called average field conditions will be as follows: for controlling weeds for the few months of growing season in crop of average phytotoxic susceptibilities such as com the rate will generally range from one to eight pounds per acre. Where weeds are to be eradicated from a more herbicideresistant crop such as sugar cane, the rate of application will range from three to twelve pounds per acre while where the weeds to be eradicated are especially resistant, mature plants of several years growth or long term total sterilization up to two to five years is desired, a range of ten to one hundred pounds per acre or higher may be used. Obviously, in soil sterilization, the upper limit of rate of application is largely dictated by economic considerations.

The novel compositions of this invention are derived either from the esterifioation of a phenol with 2,3,6-trichlorophenylaoetic acid or in the case of the unsubstituted phenyl ester, reacting the phenol with the 2,3,6-trich1orophenyl-acetyl chloride preferably in the presence of a base.

To illustrate the workings of this invention, representative non-limitative examples wherein all temperatures are in degrees centigrade and all parts are by weight unless otherwise specified, of the preparations, formulations and use of the invention are given below.

Example 1.-Phenyl 2,3,6-trichlorophenylacetyl Five parts of 2,3,6-trichlorophenylacetyl chloride were dissolved in ten parts of phenol and ten parts of pyridine were added. When the heat of reaction subsided, the mixture was warmed at ninety to one hundred degrees centigrade for ten minutes. The product was taken up in ether and washed with water, then washed with dilute hydrochloric acid, and again with Water, and finally, was stripped of solvent. The crude product was distilled and boiled at one hundred and fifty-five degrees oentigrade (0.2 millimeter of mercury). The distillate was recrystallized from methanol to yield eighty percent of a colorless crystalline solid, having a melting point of fifty-nine to sixty-one degree centigrade.

Analysis.--C-alculated for C H Cl O Found: Cl, 34.8.

Example 2.Phenyl 2,3,6-trichlorophenylacetate (alternate method) A mixture of forty-eight parts of 2,3,6-trichlorophenylacetic acid, fifty-six parts of phenol, two parts of concentrated sulfuric acid, and three hundred and fifty parts of xylene were refluxed and water was removed by continuous decantations of the distillate. After twelve hours of refluxing, the reaction mixture was washed with dilute sodium carbonate and with water, then stripped free of xylene and phenol, and the product distilled. The yield was fifty-six parts of phenyl 2,3,6-trichlorophenylacetate, having a boiling point one hundred and fifty-seven to one hundred and sixty-three degrees centigrade (at 0.35 millimeter of mercury), and a melting point of fifty-eight to sixty degrees centigrade (after recrystallization, melting point was 61.6 to 62.4 degrees centigrade).

Analysis.-Calculated for C H Cl O Cl, Found: Cl, 34.8.

Example 3.-Pentachlor0phenyl 2,3,6-trichlorophenylacetate Twenty-five parts of 2,3,6-trichlorophenylacetyl chloride, fifty-two parts of pentachlorophenol, twenty parts of pyridine, and two hundred parts of benzene were refluxed for one-half hour, the mixture filtered hot, the filtrate CmHaClgOzl Cl,

Example 4 By similar procedures the following aryl esters were 6 Example 7 Comparative volatility tests were made as follows: Healthy tomato plants of four to six inch height were individually covered by inverted four thousand milliliter beakers. Under each beaker was placed an open one hundred millimeter petri dish containing a circle of blotting paper impregnated with one gram of the various test compounds. The paper was not in contact with any part of the plant nor the soil in which the plant was growing.

prepared: 10 After two days, the tomato plants were examined for Compound Melting Boiling Percent 01 Percent Cl Point 0.) Point 0.) Calculated Found p-Chlorophenyl 2,3,fi-trichlorophenylacetate 72-3 4185-192) 40. 6 38. 3

. mm. o-Ghlorophenyl 2,3,G-trichlorophenylacetate 83-84 (0153-189) 40. 6 37 mm. 2,4-dichlorophenyl 2,3,G-trichlorophenylacetate 7S-81 0 2 185) 46. 3 45.

. mm. 2,4,5-trich1oropheny1 2,3,fi-trichlorophenylacetate 132-8 (0 35 202) 49. 9 49. 2

mm. 2,4,6-trichloropheny1 2,3,fi-trichlorophenylacetate.- 114-116 (0 3159-200) 49. 9 49. 8

. mm. o-Hydroxyphenyl 2,3,G-trichlorophenylacetate 95-100 (0 3183-6) 32. 2 29. 4-.

. mm. fl-Naphthyl 2,3,G-trichlorophenylacetate 73. 5-76. 5 29.1 29. 0 a-Naphthyl 2,3,6-tnchlorophenyl-acetate 127-127. 5 a. 29.1 28. 6 p-Tert-butyhphenyl 2,3,fi-trichlorophenylaceta 92-93 (0.1 mm.) 28. 7 27. 3 0C arboxyphenyl- 2,3,fi-trichlorophenylacetate Gum oand p-Octylphenyl 2,3,6-trichlorophenylaeetate. (0 2 203) 25.0 24. 2

* mm.=millimeters of mercury absolute pressure.

Example 5 symptoms of phytotoxicity caused by exposure to the vapors of the test compounds. Severe epinasty and leaf curling was noted with the methyl, ethyl, isopropyl and n-butyl esters of 2,3,6-trichlorophenylacetic acid and with the free acid. At most, a trace of deformation was noted plots 35 with the plants thus exposed to the phenyl, cresyl, and

B-naphthyl esters of 2,3,6-trichlorophenylacetic acid.

AVERAGE WEED COUNT RELATIVE TO CONTROL (PERCENT) Chemical Lambs Ragweed Witchgrass Plaintain Ryegrass Quarters Phenyl 2,3,6-trich1orophenylacetate 5 0 0 0 30 2-hydroxyethyl-2,3,fi-trichlorophenylacetate 4O 5 20 O 60 2-butoxyethyl 2,3,6-trichlorophenylacetate 20 0 20 10 60 Sodium 2,3,6-trichlorophenylacetate -30 0 20 0 6O 2,3,Mrichlorophenylacetic acid 20-30 0 20 0 p-Ohlorophenyl dimethyl urea (commercial herbicide) 20 10 20 90 10 Control 100 100 100 100 100 These data indicate the high activity of the phenyl ester on both broad leaf weeds and seeded grasses.

Example 6 Tests similar to those described in the above example were run at the rate of four pounds of active ingredients per acre.

CONTROL RATING 1=slight control. 2=lair control. 3=g0od control. 4= 100% control.

What is claimed is:

1. A method for controlling the growth of plants which comprises applying to the locus to be treated a herbicidal amount of phenyl 2,3,6-trichlorophenylacetate.

2. A method for controlling the growth of plants which comprises applying to the locus to be treated a herbicidal amount of a composition comprising a diluent and phenyl 2,3,6-trichlorophenyl'acetate.

3. A method according to claim 2 wherein about 4 pounds per acre of phenyl-2,3,6-trichl0rophenylacetate are applied pre-emergent.

References Cited by the Examiner UNITED STATES PATENTS 2,577,969 12/1951 Jones 71-2.6 2,977,212 3/1961 Tischler 71-216 3,077,394 2/1'963 Josephs 21-2.6

OTHER REFERENCES Marth et aL: Botanical Gazette, June 1949, pages 632 to 636.

McNew et al. 205 (1950). ELBERT L. ROBERTS, Primary Examiner. JAMES O. THOMAS, JR., Examiner.

: Iowa State Coll, J. Sci, 2 4, No. 2, page UNITED STATES PATENL' our CERTIFICATE OF CORRECTION Patent No. 3,318,682 May 9, 1967 Jack S. Newcomer et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 21 for "ts" read its line 35 for "phenyl" read N phenyl lines 68 and 69 for "suprising" read surprising column 2, line 13, for "dstances" read distances line 18, for "ester" read esters line 24, for "volatiltiy" read volatility line 47 for "partcularly" read particularly line 58, for "herbiicdal" read herbicidal column 3, line 39, for "capstan" read captan column 4, line 35, for "trichlorophenylacetyl", in italics, read trichlorophenylacetate in italics; line 48, for "degree" read degrees column 5 in the table for Example 6 second and third columns, line 1 thereof, for "Pre-emergency", each occurrence, read Pre-emergence Signed and sealed this 17th day of December 1968,

(SEAL) Atte'st:

EDWARD M.FLETCHER,JR, EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD FOR CONTROLLING THE GROWTH OF PLANTS WHICH COMPRISES APPLYING TO THE LOCUS TO BE TREATED A HERBICIDAL AMOUNT OF PHENYL 2,3,6-TRICHLOROPHENYLACETATE. 